The present invention relates to a process for producing a cycloalkanone from a cycloalkane using molecular oxygen in the presence of a particular oxidizing catalyst.
Among cycloalkanones, cyclohexanone is a compound useful in producing xcex5-aminocaprolactam which is a raw material for nylon. It is known that, in the production of cyclohexanone, in the liquid phase, cyclohexane is oxidized with molecular oxygen or a molecular oxygen-containing gas in the presence of a soluble cobalt salt as a catalyst (e.g., cobalt 0.1 to 100 ppm) to form cyclohexanone and cyclohexanol, followed by the conversion of the by-produced cyclohexanol into a cyclohexanone by subjecting the cyclohexanol to a dehydrogenating reaction using a dehydrogenator (xe2x80x9cHandbook of Chemistry: Applied Chemistryxe2x80x9d page 536, Oct. 15, 1986 version, edit by Nippon Kagaku-kai, published by Maruzen).
However, a conventional process not only involves the generation of a large amount of by-products but also pose a problem of low production rate of cyclohexanone, and further requires the by-produced cyclohexanol be treated by dehydrogenation. Moreover, when nitric acid or the like is employed for the oxidation of a cycloalkane, the process requires the use of an expensive exhaust gas-treatment facilities. Therefore, despite the process being complicated, a cyclohexanone cannot be obtained with high efficiency.
Thus, an object of the present invention is to provide a process capable of producing cycloalkanones high production rates through a sequence of steps.
Another object of the present invention is to provide a process capable of efficiently producing cycloalkanones through a sequence steps without subjecting a by-produced cycloalkanol to a dehydrogenating step.
Still another object of the present invention is to provide a process capable of producing, under mild or moderate conditions, cycloalkanonesat high conversions and selectivities without requiring the treatment of exhaust gas.
The inventors of the present invention made intensive and extensive studies to achieve the above objects, and finally found that a cycloalkanone can be efficiently formed by oxidizing a cycloalkane in the presence of a specific oxidizing catalyst (oxidation catalyst) through a series of steps. The present invention was accomplished based on the above findings.
That is, the present invention is a process for producing cycloalkanones from cycloalkanes using an oxidizing catalyst having an imide unit represented by the following formula (I): 
wherein X represents oxygen atom or hydroxyl group,
which comprises (A) a step for bringing a cycloalkane into contact with molecular oxygen in the presence of the aforementioned oxidizing catalyst, (B) a step(s) for separating the catalyst, and a by-produced acid component or a derivative thereof from the reaction mixture, and (C) steps for separating the cycloalkane, a cycloalkanol, and a cycloalkanone from the reaction mixture.
Further, from the reaction mixture may be separated a lower-boiling point component comprised of the cycloalkane, and a higher-boiling point component comprised of the cycloalkanone and the cycloalkanol. The cycloalkanone and cycloalkanol may be separated from the higher-boiling point component, and the cycloalkane and lower-boiling point impurities may further be separated from the lower-boiling point component. Further, the cycloalkanone, cycloalkanol, and higher-boiling point impurities may be separated from the higher-boiling point component. The acid component or a derivative thereof may be separated by extraction, hydrolysis, saponification, or neutralization. The cycloalkanone and the cycloalkanol, and the acid component or derivative thereof treated by means of extraction, hydrolysis, saponification or netralization may be separated from the reaction mixture individually. The reaction can be effected in the presence of a solvent, and in that case, the solvent may be separated from the reaction mixture.
The process of the present invention may comprise (A) the oxidation step, (i) a step for separating a lower-boiling point component, a higher-boiling point component, and a component containing the oxidizing catalyst, a by-produced acid component, and a derivative of the acid component by distillation; (ii) a step for separating the cycloalkane from the lower-boiling point component and then recycling the separated cycloalkane to the oxidizing reaction system; and (iii) a step for separating the cycloalkanol from the higher-boiling point component and then recycling the separated cycloalkanol to the oxidizing reaction system. The oxidizing catalyst may be separated from the component containing the oxidizing catalyst, the by-produced acid component and a derivative thereof and then recycled to the oxidizing reaction system. There is the option of carrying out the reaction in the presence of a solvent. In that case, the solvent may be separated from the reaction mixture and recycled to the oxidizing reaction system. By-produced water may be separated from the lower-boiling point component, with which water the acid component or a derivative thereof may be treated by at least one means selected from extraction, hydrolysis, saponification, and neutralization. These steps may be carried out continuously.
As the cycloalkane, a C4-10cyclohexane (particularly, cyclohexane) can be used, and the oxidizing catalyst may be used together with a co-oxidizing agent.